Atmospheric Rivers - Horizontal Moisture Transport
Atmospheric Rivers (AR), a term created at MIT in a paper by Zhu and Newell (1998), refers to the water vapour-rich part of the broader warm conveyor belt that is found in extratropical cyclones. The blended TPW product below (Figure 2) shows such an AR over the Atlantic. Because water vapour is transported in relatively narrow bands, the term Atmospheric River is quite descriptive.
Figure 2: The NOAA NESDIS operational blended TPW product. The red line circumscribes an atmospheric river heading towards Europe, 7 February 2014.
AR can be several thousand kilometres long but only a few hundred wide. Horizontal moisture transport combined with lifting processes often results in heavy precipitation events as will be shown in the next example. TPW products give complementary information on global repartition and origin of moist air masses and the way they are conveyed.